FUNCTIONAL DEFICITS IN AUTISTIC DISORDER - CHARACTERIZATION BY TECHNETIUM-99M-HMPAO AND SPECT

Autistic disorder is an early and severe developmental disorder charac terized by deficits in verbal and nonverbal language, social skills, c ognitive functioning and an abnormal repertoire of behaviors. Current research, however, has failed to identify the neurobiological mechanis ms that underlie autism or those cortical brain regions, if any, that are abnormal. Methods: We examined regional cerebral blood flow (rCBF) in six young, severely autistic patients. High-resolution brain SPECT with Tc-99m-HMPAO was performed while five of the six patients were u nder general anesthesia. The scans reflected the subjects' rCBF in the ir usual alert behavioral state, since the tracer was injected at leas t 15 min prior to anesthesia and is rapidly extracted and fixed in the brain. A computer-automated cortical region of interest (ROI) generat or was used to define 12 annular cortical regions (region 1 = left fro ntal, clockwise to region 12 = right frontal) for count data acquisiti on. The ratio of average counts in each ROI to whole-slice counts for the autistic patients was compared to age-matched controls using repea ted measures (split-plot) ANOVA statistical analysis for three represe ntative brain levels. Results: In the autistic patients, cortical regi ons 3, 4, and 10 were abnormally low at the cortical level canthomeata l (CM) + 3.5 cm. At level CM + 5.5 cm, regions 3, 4, 5 and 10 were abn ormally tow, and at level CM + 7.5 cm, regions 7 and 9 were also abnor mally low. These regions correspond to abnormally low rCBF values loca ted predominately in the temporal and parietal lobes, with the left ce rebral hemisphere showing greater rCBF abnormalities than the right. C onclusion: Our findings suggest that the temporal and parietal lobes h ave abnormal rCBF in autism. HMPAO brain SPECT in combination with gen eral anesthesia is particularly useful for imaging severely noncomplia nt patients.